Propellant stabilizer

ABSTRACT

and the propellant comprises a compound of formula 1 and an energetic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Australian Provisional Patent Application No. 2017904667, which is incorporated herein by reference in its entirety.

FIELD

The invention relates generally to propellant stabilizers and propellants comprising propellant stabilizers. The invention also relates to methods of producing a propellant comprising a propellant stabilizer as well as an ammunition cartridge comprising the stabilized propellant.

BACKGROUND

Propellants comprising energetic material are used in ammunition cartridges and in other applications for generating a propellant gas to propel a projectile. Propellants such as nitrocellulose and nitrate ester based propellants gradually decompose with age, producing acidic nitrates and nitrogen oxides. These compounds of degradation may catalyze further decomposition of the propellant, which can then lead to autocatalytic decomposition of the propellant. In the context of ammunition, this autocatalytic decomposition can in turn lead to combustion, deflagration or explosion or failure of the ammunition, resulting in shortening of the service life of the propellant-containing product.

A propellant stabilizer is typically added to the energetic material of a propellant in order to prevent or reduce the rate of decomposition, thereby prolonging the service life of the propellant. Propellant stabilizers act by scavenging the acidic nitrates and nitrogen oxides produced to form nitrosated and nitrated derivatives.

An example of a commonly used propellant stabilizer is diphenylamine (DPA). DPA is stable over long periods and is effective in stabilizing nitrocellulose-based propellants, nitrocellulose being the major energetic component of most small arms propellants. However, DPA is toxic, which makes it a chemical of concern. In particular, DPA is toxic if swallowed, inhaled or in contact with skin.

It is an object of the present application to provide a useful alternative to DPA that is suitable for use as a propellant stabilizer. In preferred embodiments, it is desired that the propellant stabilizer has a lower toxicity that DPA, providing a safer alternative to the use of DPA in propellants.

SUMMARY

Accordingly, in a first aspect of the present invention, there is provided a propellant stabilizer comprising a compound of formula 1

wherein R¹ is selected from the group consisting of H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R² is selected from the group consisting of —H, —OH, —O—(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R³ is selected from the group consisting of —H and —C₁₋₄alkyl; and R⁴ is selected from the group consisting of —H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; wherein at least one of R¹, R² and R⁴ is OH.

The present applicant previously identified that 4-(4-hydroxyphenyl)butan-2-one can act as a burn deterrent (i.e. a burn rate modifier) when applied to granules of propellant as a coating. The applicant has surprisingly found that 4-(4-hydroxyphenyl)butan-2-one, and derivatives thereof within formula 1, are capable of acting as propellant stabilizers. This finding was not expected, as preliminary tests used to indicate likely efficacy as a stabilizer did not indicate that the compound had stabilizing properties. However, subsequent work conducted by the inventors did show that the compound does have stabilizing properties. In fact, the new propellant stabilizer is capable of stabilizing energetic materials such as nitrocellulose to a comparable extent as and to a greater extent than the commonly used propellant stabilizer DPA, making it suitable for use in propellants and ammunition cartridges. The new propellant stabilizer also has a more favourable toxicity profile compared to DPA, making the workplace environment safer for those involved in propellant and ammunition manufacture.

According to a second aspect, there is also provided the use of the compound of formula 1 as a propellant stabilizer.

In some embodiments, the compound of formula 1 is 4-(4-hydroxyphenyl)butan-2-one. Although this compound is preferred, it is appreciated that closely structurally and physical property-related compounds may also provide further alternative propellant stabilizers to DPA. In some embodiments, the compound of formula 1 is 4-(4-hydroxy-3-nitrophenyl)butan-2-one.

According to a third aspect, there is provided a propellant comprising an energetic material; and a compound of formula 1

wherein R¹ is selected from the group consisting of H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R² is selected from the group consisting of —H, —OH, —O—(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R³ is selected from the group consisting of —H and —C₁₋₄alkyl; and R⁴ is selected from the group consisting of —H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; wherein at least one of R¹, R² and R⁴ is OH; and wherein the compound is dispersed evenly throughout the energetic material.

In a fourth aspect, there is provided an ammunition cartridge comprising the propellant described above.

The ammunition cartridge typically comprises a casing, the propellant described above, a primer and a projectile. The ammunition may also contain boosting charges and tracer compounds.

According to a fifth aspect, there is provided a method of preparing a propellant, comprising dispersing a compound of formula 1

wherein R¹ is selected from the group consisting of H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R² is selected from the group consisting of —H, —OH, —O—(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R³ is selected from the group consisting of —H and —C₁₋₄alkyl; and R⁴ is selected from the group consisting of —H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; and wherein at least one of R¹, R² and R⁴ is OH evenly throughout an energetic material and granulating the energetic material.

These aspects are described more fully in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail, by way of example only, with reference to the following Figures:

FIG. 1 is a schematic illustration of a granule of the propellant composition containing 4-(4-hydroxyphenyl)butan-2-one according to one embodiment of the invention.

FIGS. 2A through 2E present graphs showing normalised heat flow for propellant formulations containing DPA, DPA and 4-(4-hydroxyphenyl)butan-2-one, or 4-(4-hydroxyphenyl)butan-2-one (FIGS. 2A, 2B and 2C); and normalised heat flow for propellant formulations containing either DPA or 4-(4-hydroxyphenyl)butan-2-one as the stabilizer (FIGS. 2D and 2E).

FIGS. 3A through 3C present chromatography traces of aged propellant formulations incorporating 4-(4-hydroxyphenyl)butan-2-one (FIGS. 3A and 3B) compared with a propellant formulation containing only DPA as the stabilizer (FIG. 3C).

FIGS. 4A through 4D present chromatography traces of an aged propellant formulation incorporating 4-(4-hydroxyphenyl)butan-2-one (FIG. 4A), synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one (FIG. 4B), the aged propellant formulation spiked with synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one (FIG. 4C), and a mass spectrum of the 3.6 min peak (FIG. 4D).

FIGS. 5A and 5B present ¹H NMR spectra of an extract from an aged propellant formulation containing 4-(4-hydroxyphenyl)butan-2-one as the stabilizer (FIG. 5A) compared with synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one (FIG. 5B).

DETAILED DESCRIPTION

The invention relates generally to propellant stabilizers and propellants comprising a propellant stabilizer. The invention also relates to methods of producing a propellant comprising a propellant stabilizer as well as an ammunition cartridge comprising the stabilized propellant.

In the following, we have described features of the method and the propellant stabilizer and propellant. All features described below apply independently to the methods and the products of the invention.

Compounds

The present invention involves the use of a compound of formula 1

wherein R¹ is selected from the group consisting of H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R² is selected from the group consisting of —H, —OH, —O—(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R³ is selected from the group consisting of —H and —C₁₋₄alkyl; and R⁴ is selected from the group consisting of —H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄ alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; and wherein at least one of R¹, R² and R⁴ is OH.

In some embodiments R¹ is selected from the group consisting of OH, O—(C₁₋₄-alkyl) and C₁₋₄alkyl. In other embodiments, R¹ is selected from the group consisting of OH and O—(C₁₋₄alkyl). In a particularly preferred embodiment, R¹ is OH.

R¹ may be in any position around the aromatic ring. For example, R¹ may be in the ortho, meta or para position. In some embodiments, R¹ is in the para position.

In some embodiments, R² is selected from the group consisting of H, OH, O—(C₁₋₄alkyl) and C₁₋₄alkyl. In other embodiments, R² is selected from the group consisting of H, OH and O—(C₁₋₄alkyl). In a particularly preferred embodiment, R² is H.

In some preferred embodiments, R³ is H.

In some embodiments, R⁴ is selected from the group consisting of H, —NO₂, OH, O—(C₁₋₄alkyl) and C₁₋₄alkyl. In other embodiments, R⁴ is selected from the group consisting of H, —NO₂, OH and O—(C₁₋₄alkyl). In a particularly preferred embodiment, R⁴ is H. In some embodiments, R⁴ is —NO₂.

R⁴ may be in any position around the aromatic ring. For example, R⁴ may be in the ortho, meta or para position. In some embodiments, R⁴ is in an ortho or meta position.

In one embodiment, R¹ is OH, R² is H, R³ is H and R⁴ is H.

In one embodiment, R¹ is OH, R² is H, R³ is H and R⁴ is —NO₂.

The term C₁₋₄alkyl refers to a branched or unbranched alkyl group having from one to four carbon atoms inclusive. Examples of C₁₋₄alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl. This definition applies to references to C₁₋₄alkyl alone or as part of a substituent such as —O(C₁₋₄alkyl), —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂ or —N(C₁₋₄alkyl)NH₂.

Propellant Stabilizer

The compound of formula 1 functions as a propellant stabilizer. The term “stabilizer” refers to any compound which can be used to stabilize the energetic material.

The compound of formula 1 is present in the propellant in an amount which is sufficient to retard the decomposition of the energetic material compared with the decomposition rate without the presence of the compound. In some embodiments, the compound of formula 1 is present in amounts of from about 0.1 to about 10% by weight of the propellant. For example, the compound of formula 1 may be present in an amount of about 0.2 to about 8%, such as about 0.5 to about 6.5%, or about 0.7 to about 6%. Preferably, the compound of formula 1 is present in an amount of about 1 to about 5% by weight of the propellant. Most preferably, the compound of formula 1 is present in an amount of about 1 to about 2% by weight of the propellant.

The compound of formula 1 preferably has a melting point of about 50 to about 90° C. For example, the melting point may be about 55 to about 85° C., such as about 60 to about 80° C., or about 65 to about 75° C. In some embodiments, the compound of formula 1 has a melting point of at least about 50° C. For example, the melting point may be at least about 60° C., such as at least about 65° C., or at least about 70° C.

In some embodiments, the compound of formula 1 is 4-(4-hydroxyphenyl)butan-2-one.

Although this compound is preferred, it is appreciated that closely structurally and physical property-related compounds may also perform as per 4-(4-hydroxyphenyl)butan-2-one.

In some embodiments, the compound of formula 1 is 4-(4-hydroxy-3-nitrophenyl)butan-2-one.

Tests were conducted by the applicant demonstrating the efficacy of 4-(4-hydroxyphenyl)butan-2-one as a propellant stabilizer. The long-term tests showed that 4-(4-hydroxyphenyl)butan-2-one is capable of stabilizing energetic materials such as nitrocellulose over extended periods of time. In fact, 4-(4-hydroxyphenyl)butan-2-one is capable of stabilizing nitrocellulose-based propellants to a comparable extent as or a greater extent than commonly used propellant stabilizer DPA. Advantageously, 4-(4-hydroxyphenyl)butan-2-one does not have the drawbacks of toxicity associated with DPA. The compounds of the invention provide useful alternatives to DPA and other stabilizers currently in use to provide new propellant compositions.

The propellant may also comprise a second stabilizer. The second stabilizer(s), which is different to the first stabilizer, may be selected from the group consisting of a second compound of formula 1, sodium hydrogen carbonate, calcium carbonate, magnesium oxide, akardites, centralites, 2-nitrosodiphenylamine, diphenylamine, N-methyl-p-nitroaniline and combinations thereof.

Energetic Material

The propellant of the present invention comprises an energetic material. The term “energetic material” includes any material which can be burned to generate a propellant gas to propel a projectile.

In some embodiments, the energetic material is selected from the group consisting of black powder, ammonium perchlorate, hexogen, butanetrioltrinitrate, ethyleneglycol dintrate, diethyleneglycol dinitrate, erithritol tetranitrate, octogen, hexanitroisowurtzitane, metriol trinitrate, N-methylnitramine, pentaerythritol tetranitrate, tetranitrobenzolamine, trinitrotoluene, nitroglycerine, nitrocellulose, mannitol hexanitrate, triethylene glycol dinitrate, guanidine, nitroguanidine, 3-nitro-1,2,4-triazol-5-one, ammonium nitrate, propanediol dinitrate, hexamine, 5-aminotetrazole, methyltetrazole, phenyltetrazole, polyglycidylnitrate, polyglycidylazide, poly[3-nitratomethyl-3-methyloxitane], poly[3-azidomethyl-3-methyloxitane], poly[3,3-bis(azidomethyl)oxitane], nitrated cyclodextrin polymers, poly glycidylnitrate, and combinations thereof.

In some specific embodiments, the energetic material is selected from the group consisting of nitroglycerine, nitrocellulose and combinations thereof.

In some embodiments, the propellant comprises a single energetic material. For example, the propellant may only comprise nitrocellulose. In such circumstances, the energetic material may be referred to as “single base” and the propellant may be referred to as “a single base propellant”. In other embodiments, the propellant may comprise two energetic materials. For example, the propellant may comprise nitrocellulose and nitroglycerin. In such cases, the energetic material may be referred to as “double base” and the propellant may be referred to as “a double base propellant”. In still other embodiments, the propellant may comprise more than two energetic materials. For example, the propellant may comprise nitrocellulose, nitroguanidine and nitroglycerin. In such circumstances, the energetic material may be referred to as “multiple base” and the propellant may be referred to as “a multiple base propellant”.

In one embodiment, the energetic material is nitrocellulose.

The energetic material may be in any form that is suitable for incorporation into an ammunition cartridge for a firearm.

The Propellant

The propellant comprises an energetic material and a compound of formula 1. The energetic material and compound of formula 1 may be combined in any way, provided that the compound of formula 1 is dispersed throughout the energetic material. Preferably, the compound of formula 1 is dispersed evenly throughout the energetic material. In other words, the concentration of the propellant stabilizer is approximately the same throughout the energetic material. The compound of formula 1 can be used in conjunction with other established stabilizing compounds to suit the formulator.

In some embodiments, the energetic material and the compound of formula 1 are in the form of granules. The term “granule” may also be referred to as “kernel” or “pellet”. Incorporation of the compound of formula 1 throughout the energetic material can be achieved by forming a slurry or dough of the energetic material and the compound. For example, the energetic material and the compound of formula 1 can be blended together in a mixer. The resulting mixture can then be formed into granules.

The granules of energetic material and the compound of formula 1 may be prepared by any method known in the art. For example, a slurry or dough of energetic material and the compound of formula 1 may be extruded. In another embodiment, the energetic material and the compound of formula 1 in particulate form may be compressed into a granule. In another embodiment, particulates of energetic material and the compound of formula 1 may be coalesced and shaped into agglomerates by pumping a slurry through shaping tubes. In some embodiments, the agglomerates may be substantially spherical in shape. The agglomerates may be referred to as particles.

In one embodiment, the granules are prepared by extruding a slurry or dough of energetic material and the compound of formula 1 to form an extrudate, and granulating the extrudate. The term “granulating” refers to the process of dividing, or cutting, an extrudate into granules. In some embodiments, the slurry or dough of energetic material and the compound of formula 1 is extruded, for example using an extrusion die, to form an extrudate cord, and the extrudate cord is cut to the desired length to form granules. The granules may be of any size suitable for use in ammunition. The extrudate cord may be cut into the desired granule lengths immediately upon exit from the extrusion die, or at some time after the extrudate cord is formed. For example, the extrudate cord may be cut immediately as the cord extrudes or after the collection of a suitable length of cord. The cutting may be performed while the cord is still soft, or when it is dry and hard.

As a consequence of the processing steps described above, the granules may also be referred to as agglomerates, grains or particles.

The granules can be of any shape. In some embodiments, the granules have an axial dimension with a consistent cross-section. For example, the granule may have a substantially circular cross-section or the cross-section may be elliptical or any other similar shape. In some embodiments the granules are cylindrical in shape.

The granules may be of any size suitable for use in ammunition. In some embodiments, the granules are about 0.1 to about 25 mm in length. For example, the granules may be about 0.3 to about 20 mm in length, such as about 0.5 to about 12 mm in length, or about 0.7 to about 5 mm in length, or about 1 to about 2 mm in length.

In some embodiments, the granules have a diameter of about 0.1 to about 20 mm. For example, the granules may have a diameter of about 0.2 to about 15 mm, such as about 0.4 to about 12 mm, or about 0.5 to about 10 mm, or about 0.6 to about 5 mm, or about 0.7 to about 1 mm.

The granules may have a greater length than diameter. In these embodiments, the granules may be referred to as sticks. In some embodiments, the length of the sticks may be about 6 to about 14 mm, such as about 8 to about 12 mm. In some embodiments, the diameter of the sticks may be about 0.6 to about 1.2 mm, such as about 0.7 to about 1 mm.

After granulation, the granules are dried during which they may contract slightly. This contraction can be taken into account when granulating the granules or compressing the particulates of energetic material and the compound of formula 1. The contracted granules may be of any size suitable to be used in ammunition. In some embodiments, the granules are about 0.1 to about 25 mm in length. For example, the granules may be about 0.3 to about 20 mm in length, such as about 0.5 to about 12 mm in length, or about 0.7 to about 5 mm in length, or about 1 to about 2 mm in length.

In some embodiments, the granules have a diameter of about 0.1 to about 20 mm. For example, the granules may have a diameter of about 0.2 to about 15 mm, such as about 0.4 to about 12 mm, or about 0.5 to about 10 mm, or about 0.6 to about 5 mm, or about 0.7 to about 1 mm.

When the contracted granules are sticks, the length of the sticks may be about 6 to about 14 mm, such as about 8 to about 12 mm. In some embodiments, the diameter of the sticks may be about 0.6 to about 1.2 mm, such as about 0.7 to about 1 mm.

In some embodiments, the granules comprise a perforation to enhance burning rates later in the burning cycle and to make the granules more progressive in burning. Expressed another way, in some embodiments, the granules comprise one or more perforations. The term “perforation” refers to an aperture in the granule. Alternative terms for “perforation” include channel, bore and cavity.

The perforation may extend all the way through the granule. In some embodiments, the perforation extends axially through the granule.

The perforation may be of any diameter suitable for the size of the granule. In some embodiments, the perforation has a diameter of about 50 to about 1000 μm. For example, the perforation may have a diameter of about 50 to about 700 μm, such as about 50 to about 500 μm, or about 100 to about 300 μm.

There may be more than one perforation in each granule. In some embodiments, there is a single perforation. In other embodiments, there are multiple perforations. When the energetic material is made by extrusion, the extrudate may be extruded with one or more perforations.

Additional Layers

The propellant may comprise additional layers. Suitable layers include a layer of a burn rate modifier, a finishing layer, an ignition layer and/or a layer of a second energetic material.

In embodiments where there is a layer of a burn rate modifier, the burn rate modifier may be in the form of a coating on granules of the energetic material. In embodiments where the granules comprise a perforation, the burn rate modifier layer may also coat the exposed area of the perforation(s). The coating of the energetic material may be performed by any method known in the art. The burn rate modifier coating material may be any burn rate modifier known in the art. Examples of suitable burn rate modifiers include, but are not limited to, dinitrotoluene, acetyl triethyl citrate, triethyl citrate, tri-n-butyl citrate, tributyl acetyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n-hexyl citrate, n-butyryl tri-n-hexylcitrate, di-n-butyl adipate, diisopropyl adipate, diisobutyl adipate, diethylhexyl adipate, nonyl undecyl adipate, n-decyl-n-octyl adipate, dibutoxy ethoxy ethyl adipate, dimethyl adipate, hexyl octyl decyl adipate, diisononyl adipate, dibutyl phthalate, diethyl phthalate, diamyl phthalate, nonylundecyl phthalate, bis(3,5,5-trimethylhexyl) phthalate, di-n-propyladipate, di-n-butyl sebacate, dioctyl sebacate, dimethyl sebacate, diethyl diphenyl urea, dimethyl diphenyl urea, di-n-butyl phthalate, di-n-hexyl phthalate, dinonyl undecyl phthalate, nonyl undecyl phthalate, dioctyl terephthalate, dioctyl isophthalate, 1,2-cyclohexane dicarbonic acid diisononylester, dibutyl maleate, dinonyl maleate, diisooctyl maleate, dibutyl fumarate, dinonyl fumarate, dimethyl sebacate, dibutyl sebacate, diisooctyl sebacate, dibutyl azelate, diethylene glycol dibenzoate, trioctyl trimelliate, trioctyl phosphate, butyl stearate, methylphenylurethane, N-methyl-N-phenylurethane, ethyl diphenyl carbamate, camphor, gum Arabic, gelatin, rosin, modified rosin esters, resins of dibasic acids and alkyl fatty alcohols, polyesters of molecular weight 1500-30,000 based on dihydric alcohols and dibasic acids, and combinations thereof. Alternatively, the burn rate modifier coating material can be a compound of formula 1. In this embodiment, granules of propellant would comprise the compound of formula 1 distributed throughout each granule of energetic material with or without other co-stabilizing compounds, and a higher concentration of the compound of formula 1 in an outer region of the granule consistent with the coating of the granules with additional compound of formula 1.

In embodiments where there is a layer of second energetic material, the energetic material that forms the core of the propellant will be referred to as a first energetic material. The layer of second energetic material can be selected from the range of energetic materials described above. The layer of second energetic material is suitably different to the first energetic material.

In embodiments where the propellant comprises an ignition layer, the ignition layer comprises an ignition component. The ignition component may comprise a group I metal salt of nitrate.

In embodiments where the propellant comprises a finishing layer, the finishing layer may be in the form of a graphite layer. Surface-graphiting is typically the final finishing step, yet graphiting may be completed prior to or after drying the propellant. In some embodiments, the graphite finishing layer may comprise an ignition component. Examples of suitable ignition components include one or more group I metal salt of nitrate.

The finishing layer is generally the outermost layer on the propellant. The additional layers may be complete layers around the propellant or they may be partial layers.

Additives

In some embodiments, the propellant further comprises an additive selected from the group consisting of plasticizers, flash suppressants, barrel-wear ameliorants and combinations thereof.

In some embodiments, the additive is incorporated within the granules of the is energetic material and the compound of formula 1. In other embodiments, the additive is incorporated in the additional layer(s) of the propellant. Incorporation of the additive within the granules of energetic material and the compound of formula 1 can be achieved by adding the additive to the slurry or dough of energetic material and the compound, which is then formed into granules.

The term “plasticizer” refers to any compound which imparts homogeneity and plasticity to the energetic material. In some embodiments, the plasticizer may be selected from the group consisting of diethylphthalate, camphor, dibutylphthalate, di-n-propyl adipate, methylphenyl urethane, calcium stearate, butyl stearate, nitroglycerin, glyceroltribenzoate and combinations thereof.

The term “flash suppressant”, refers to any compound which can be used to suppress the muzzle flash of a firearm. In some embodiments, the flash suppressant may be selected from the group consisting of potassium and ammonium salts of organic and/or inorganic acids, potassium sulphate, potassium nitrate, potassium carbonate, potassium bicarbonate, potassium tartrate, potassium bitartrate, ammonium bicarbonate, ammonium carbonate and combinations thereof.

The term “barrel-wear ameliorants” refers to any compound which can be used to reduce barrel-wear. In some embodiments, the barrel-wear ameliorant may be selected from the group consisting of bismuth, bismuth oxide, bismuth citrate, bismuth subcarbonate, lead, lead carbonate, other salts of lead and bismuth and combinations thereof.

FIG. 1 is a schematic illustration of the propellant according to one embodiment of the invention, in which the propellant is in the form of a granule of energetic material with the stabilizer of the invention dispersed throughout (1). The granule of energetic material and stabilizer is coated with a layer of a burn rate modifier (2). The propellant further comprises an ignition layer (3). Such propellant cross-sections may or may not require perforations, depending on the geometry of the designed propellant.

Without limiting the techniques used to form a propellant, the propellant granule of FIG. 1 may be prepared by forming a dough or slurry of the energetic material and the stabilizer of the invention, extruding the dough or slurry to form an extrudate cord, and then cutting the extrudate cord to the required length. The extruded cord can have any length at the time of cutting, meaning the cord can be extruded to metres, centimetres, millimetres or microns in length prior to cutting. The extruded lengths may be cut to any useful length known to be suitable for propellant applications. After further processing to remove unwanted solvents from the formulation, the granule may then be coated in a layer of burn rate modifier, and finally coated with the ignition or is finishing layer.

Ammunition

In one embodiment, there is provided an ammunition cartridge comprising the propellant. The ammunition cartridge typically comprises a casing, the propellant described above, a primer and a projectile.

The propellant of the present invention is suitable for use in a wide range of firearms. It is particularly suitable for use in .22-.224 calibre firearms, .243 calibre firearms, .27 calibre firearms, 6 mm calibre firearms, 7 mm calibre firearms .30 calibre firearms, 8 mm calibre firearms, .338 calibre firearms up to .50 calibre firearms and is even suitable for medium to large calibre firearms.

The casing may be made of any material of sufficient strength and thickness to not rupture during burning of the propellant. The casing may be of any size and the size will depend upon the firearm in which the cartridge is to be used. Conventional casing materials and construction is well known in the art and applies to the present application.

The primer, or priming compound, may be comprised of any substance which is capable of igniting the propellant on initiation. Examples of priming compounds include but are not limited to lead azide (dextrinated), lead styphnate, mercury fulminate and combinations thereof. In some embodiments, the priming compound is ASA (aluminium, lead styphnate, lead azide).

The projectile may be any object which can be projected from the muzzle of a firearm system (or gun) upon burning of the propellant. Examples of projectiles include, but are not limited to, bullets, shot, pellets, slugs, shells, balls, buckshot, bolts, rockets and cannon balls. In some embodiments, the projectile is selected from the group consisting of a bullet, pellet, slug and ball.

Advantages

The compounds of formula 1 contain only carbon, hydrogen, oxygen and in some cases nitrogen and do not contain any potentially toxic or hazardous elements such as halogens. The compounds are capable of stabilizing energetic materials such as nitrocellulose over extended periods of time. In fact, the compounds are capable of stabilizing energetic materials such as nitrocellulose to a comparable extent as or a greater extent than commonly used propellant stabilizer DPA, making them suitable for use in propellants and ammunition cartridges.

EXAMPLES

The invention will now be described with reference to the following non-limiting Examples.

Stabilizing effect of 4-(4-hydroxyphenyl)butan-2-one Preliminary Tests

Methyl Violet Paper (MVP) and Abel Heat tests were conducted on samples of small nitrocellulose-based propellants containing 4-(4-hydroxyphenyl)butan-2-one to obtain a preliminary indication as to the likely efficacy of 4-(4-hydroxyphenyl)butan-2-one as a stabilizer. The tests did not give a strong indication that that 4-(4-hydroxyphenyl)butan-2-one stabilized the propellant compositions. Nonetheless, work continued on with further tests conducted to determine whether 4-(4-hydroxyphenyl)butan-2-one has stabilizing properties.

Example 1

STANAG 4582 is a standard NATO stability test procedure for single base, double base and triple base propellants using heat flow calorimetry. Propellants that satisfy STANAG 4582 are considered to remain chemically stable for a minimum of ten years if stored at temperatures equivalent to an isothermal storage at 25° C.

Samples of nitrocellulose-based propellants without burn rate modifier (approximately 1.5 mm long, 0.8 mm outer diameter and 0.2 mm perforation) stabilized with either 1% DPA or 1% 4-(4-hydroxyphenyl)butan-2-one or a combination of the two stabilizers were compared according to the accepted STANAG 4582 method. The samples were prepared in small quantities of less than 1 kg propellant granules, with the stabilizer materials mixed evenly throughout the energetic material.

The results are set out in Table 1. FIG. 2 shows the heat flow calorimetry traces of the samples stabilized with 1% DPA (FIG. 2A) or 1% 4-(4-hydroxyphenyl)butan-2-one (FIG. 2C), or a combination (FIG. 2B).

TABLE 1 Normalised Heat Flow Sample Stabilizer Output (μW/g) Propellant I 1% DPA 8 Propellant II 0.5% DPA + 0.5% 4-(4- 18 hydroxyphenyl)butan-2-one Propellant III 1% 4-(4-hydroxyphenyl)butan-2-one 33

The results show that all three propellants fulfilled the requirements of STANAG 4582, with the 4-(4-hydroxyphenyl) butan-2-one-stabilized sample having a normalised heat flow output of 33 μW/g, compared with a normalized heat flow output of 8 μW/g for the DPA-stabilized sample. This data demonstrates that 4-(4-hydroxyphenyl)butan-2-one is capable of long term stabilization of nitrocellulose-based propellants.

Example 2

Samples of nitrocellulose-based propellants without burn rate modifier (approximately 1.5 mm long, 0.8 mm outer diameter and 0.2 mm perforation) stabilized with either 1% DPA or 1% 4-(4-hydroxyphenyl) butan-2-one were compared according to the accepted STANAG 4582 method. The samples were prepared in larger quantities of up to 5 kg propellant granules, with the stabilizer mixed evenly throughout the energetic material.

The results are set out in Table 2. FIG. 2 shows the heat flow calorimetry is traces of the samples stabilized with 1% DPA (FIG. 2D) or 1% 4-(4-hydroxyphenyl) butan-2-one (FIG. 2E).

TABLE 2 Normalised Heat Flow Sample Stabilizer Output (μW/g) Propellant A ~1% DPA 44 Propellant B ~1% 4-(4-hydroxyphenyl) butan-2-one 120

The results show that both propellants fulfilled the requirements of STANAG 4582, with the 4-(4-hydroxyphenyl) butan-2-one-stabilized sample having a normalised heat flow output of 44 μW/g, compared with a normalized heat flow output of 120 μW/g for the DPA-stabilized sample. This data demonstrates that 4-(4-hydroxyphenyl)butan-2-one is capable of long term stabilization of nitrocellulose-based propellants.

Mechanism of Stabilizing Effect of 4-(4-hydroxyphenyl)butan-2-one

FIG. 3 shows chromatography traces of nitrocellulose-based propellants (approximately 1.8 mm long, 0.8 mm diameter, 0.18 micron perforation) including 1% DPA and 6% DNT (FIG. 3A), 1% DPA and 2% 4-(4-hydroxyphenyl)butan-2-one (FIG. 3B), or 1% DPA and 6% 4-(4-hydroxyphenyl)butan-2-one (FIG. 3C), which had been aged for 40 days at 65.5° C. The traces of samples containing 4-(4-hydroxyphenyl)butan-2-one show new peaks not present in the sample containing DPA and DNT. Without wishing to be bound by theory, the inventors hypothesise that 4-(4-hydroxyphenyl)butan-2-one acts as a propellant stabilizer by scavenging acidic nitrates and nitric oxides, and that these new peaks correspond to daughter compounds derived from 4-(4-hydroxyphenyl)butan-2-one. Daughter compounds may include 4-(4-hydroxy-3-nitrophenyl)butan-2-one and 4-(4-hydroxy-3,5-dinitrophenyl)butan-2-one.

FIG. 4A shows a chromatography trace of a sample of a nitrocellulose-based propellant (1.39 mm long, 0.7 mm diameter, 50 micron perforation) including 1% 4-(4-hydroxyphenyl)butan-2-one, aged for 40 days at 65.5° C. Without wishing to be bound by theory, the inventors hypothesis that the peak at approximately 3.6 minutes corresponds to 4-(4-hydroxy-3-nitrophenyl)butan-2-one. Subsequent investigations supported this hypothesis. FIG. 4B shows a chromatography trace of a sample of synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one under the same conditions, the synthetic sample eluting at approximately 3.6 minutes. FIG. 4C shows a chromatography trace of a sample of the aged propellant formulation spiked with synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one, in which the peak at approximately 3.6 minutes was shown to have grown. FIG. 4D shows the mass spectrum of the 3.6 minute peak compound, which corresponds to the mass of 4-(4-hydroxy-3-nitrophenyl)butan-2-one. FIG. 5A shows the ¹H NMR spectrum of the 3.6 minute peak compound, which corresponds to the ¹H NMR spectrum of synthetic 4-(4-hydroxy-3-nitrophenyl)butan-2-one shown in FIG. 5B. These data indicate that 4-(4-hydroxyphenyl)butan-2-one acts as a propellant stabilizer by scavenging acidic nitrates and nitric oxides to generate daughter compound 4-(4-hydroxy-3-nitrophenyl)butan-2-one.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 

1. A propellant comprising: an energetic material; and a compound of formula 1

wherein R¹ is selected from the group consisting of H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R² is selected from the group consisting of —H, —OH, —O—(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; R³ is selected from the group consisting of —H and —C₁₋₄alkyl; and R⁴ is selected from the group consisting of —H, —OH, —O(C₁₋₄alkyl), —C₁₋₄alkyl, —NHC₁₋₄alkyl, —N(C₁₋₄alkyl)₂, —NO₂, —NHNH₂, —N(C₁₋₄alkyl)NH₂, and —CN; wherein at least one of R¹, R² and R⁴ is OH; and wherein the compound of formula 1 is dispersed evenly throughout the energetic material.
 2. The propellant according to claim 1, wherein the energetic material is in the form of granules.
 3. The propellant according to claim 1, wherein the energetic material is selected from the group consisting of black powder, ammonium perchlorate, hexogen, butanetrioltrinitrate, ethyleneglycol dintrate, diethyleneglycol dinitrate, erithritol tetranitrate, octogen, hexanitroisowurtzitane, metriol trinitrate, N-methylnitramine, pentaerythritol tetranitrate, tetranitrobenzolamine, trinitrotoluene, nitroglycerine, nitrocellulose, mannitol hexanitrate, triethylene glycol dinitrate, guanidine, nitroguanidine, 3-nitro-1,2,4-triazol-5-one, ammonium nitrate, propanediol dinitrate, hexamine, 5-aminotetrazole, methyltetrazole, phenyltetrazole, polyglycidylnitrate, polyglycidylazide, poly[3-nitratomethyl-3-methyloxitane], poly[3-azidomethyl-3-methyloxitane], poly[3,3-bis(azidomethyl)oxitane], nitrated cyclodextrin polymers, poly glycidylnitrate, and combinations thereof.
 4. The propellant according to claim 1, wherein the energetic material is nitrocellulose.
 5. The propellant according to claim 1, wherein the compound of formula 1 is 4-(4-hydroxyphenyl)butan-2-one.
 6. The propellant according to claim 1, further comprising a graphite layer.
 7. A method of preparing a propellant according to claim 1, comprising dispersing the compound of formula 1 evenly throughout an energetic material and granulating the energetic material.
 8. The method according to claim 7, wherein the granules of energetic material are formed by forming a slurry or dough of the energetic material and the compound of formula 1, extruding the slurry or dough of the energetic material and the compound of formula 1 to form an extrudate cord and cutting the extrudate cord.
 9. The method according to claim 7, wherein the compound of formula 1 is 4-(4-hydroxyphenyl)butan-2-one.
 10. An ammunition cartridge comprising a propellant according to claim
 1. 11. The ammunition cartridge according to claim 10, further comprising a casing, a primer and a projectile. 